Forwards
RF: Lionel Messi
Oh, Leo Messi.
He started La Liga 2017-18 like he wanted to win the damn thing before it even began, and although, he went through a slight slump (four games in which he didn't score - normal for most, a slump for Leo), he is back to his inimitable best.
Combine that with his impeccable Clasico record (24 goals and 13 assists - the most of any player in history) and there's no way he's not making the cut.
CF: Cristiano Ronaldo
Hah. You thought I wouldn't pick him?
Cristiano Ronaldo may not have been in the best of form in La Liga (before the presentation of his fifth Ballon d'Or - after it, against Sevilla, he was unplayable) but as he showed by setting a new record in the Champions League (scoring in every game of the group stages - the first person to do so) and by winning Madrid the much-maligned Club World Cup he is still at the peak of his considerable goalscoring powers, and it'd take an idiot to drop him from any XI he is eligble to play in
LF: Andres Iniesta
Last season, Andres Iniesta would have made this team purely on the basis of nostalgia. Over large parts of the past two seasons the great man had dwindled and diminished into a shadow of his former self, but much like with Busquets, a return to the possession-and-midfield oriented philosophy has breathed new life into him.
At times this season, Iniesta has taken the breath away with his performances and there can be no better player for this position in this combined XI
The team, then:
GK: Ter Stegen
DEF: Carvajal, Pique, Varane, Alba
MID: Kroos, Busquets, Paulinho
FW: Messi, Ronaldo, Iniesta